Signaling system



Nov. 6, 1923.

P. B. MURPHY SIGNALING SYSTEM Filed Aug. 28, 1920 2 Sheets-Sheet l NMX QV L Nov. 6, 1.923.

P. B. MURPHY SIGNALING SYSTEM Filed Aug. 28 1920 2 Sheets-Sheet 2 /n Ver; for:

Patented Nov. 6, 1923.

PAUL B. MURPHY, OF NYACK, .NEW YORK, ASSIGNOR TO WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, N.

Y., A CORPORATION OF NEW YORK.

SIGN ALIN G SYSTM.

Application led August 28, 1920. Serial No. 406,584.

To all 11i/1.0m it may come/rn:

Be it known that I, PAUL B. MURPHY, a citizen of the United States of America, residing at Nyack` in the county of Rockland, State of New York, have invented certain new and useful Improvements in Signaling Systems, of which the following iS a full, clear, concise, and exact description.

This invention relates to signaling systems and moreparticularly to methods of and means for signaling to distant stations by modified carrier waves.

It has been proposed in telephone toll line signaling to employ two sources of different frequency alternating currents and to cause these currents to be alternately applied to the line in regular sequence. At the receiving station two circuits tuned respectively to the frequencies of these two currents are arranged to control the windings of a biased polarized relay. While these currents are being applied alternately to the line, the polarized relay armature is kept in motion and thus causes the local ringing relay bell or signal lamp to be energized. When application of these two currents ceases the signal clement deenergizes.

A particular advantage of the use of this system for telephony is that the frequencies of these ringing currents may be made such that they will fall within the speech frequency range for which most efiicient transmission may be had. They are, therefore, readily handled by the ordinary telephonie transmission line elements. Moreover, the alternate frequency combination rende-rs the receiving apparatus designed therefor proof againstoperation by speech currents of the particular frequencies used for ringing for the reason that to operate the biased .polarized relay, the currents of these two frequencies must occur sequentially at the proper rate of alternation. o

The present invention has as one of its features the adaptation of this alternate fre-y quency ringing system to carrier wave transmission. In carrier wave transmission whether by unguided or by circuit guided waves, there 1s frequently a tendency for interference to occur. In radio transmission, static energy and other strays cause such interference, particularly in certain latitudes and during certain times of the year, that it has been considered practically impossible to free radio teledynamic operation from inter-ference. In guided wave transmission and particularl in multiplex signaling systems, cross ta k from other transmission channels as well as combination frequency currents produced in the signaling channel itself, when external disturbing energy is lmpressed upon the channel, may cause a false operation of the signal receiving element.

According to the present invention, a carrier wave transmission system is provided at its transmitting station with means to'cut oft' the local talking circuit from the outgoing carrier wave channel and to connect in its stead to the outgoing channel a source for alternately applying two alternating currents of different frequencies in a regular sequence. These alternately applied currents are caused to modulate the outgoing carrier wave in the same manner that it is modulated by speech currents when carrier Wave telephony is in progress. At the receiving station, the modulated carrier wave is detected or demodulated by the same apparatus used for detection of speech modulated waves 'and the detected alternate frequency currents are caused to energizeselective circuits to control the operation of adifferentially acting relay whichin turn operates the local signal element or applies the ringing signal to the receiving circuits as the case may be. By making the receiving apparatus responslble only to the conjoint I action of the predetermined frequencies applied in a predetermined' manner, the possibility of false signals being received 1s remote.

An object of the invention is toJ provide a carrier wave signaling system which will be free from interference by strays and cross talk signals. A further object of the invention is to provide means for signaling to an operator in systems in which telephone lines are connected to each other by means of carrier wave toll connections.

For an understanding of a system operating according to this invention and embodying its features, reference ma be had to the accompanying detailed description taken in connection with the annexed drawing in which Fig. 1 and Fig. 2 together illustrate, diagrammatically, signaling circuits for connecting a low frequency line to a carrier wave transmission circuit and Fi 3 illustrates a modiiication of a detail ofg. 1.

ln considering the drawing Fig. 2 should be placed at the right of Fig. 1. Referring to these figures, a standard operators cord circuit 1 is shown associated with a trunk circuit 2 which terminates in carrier wave transmitting channel 3 and carrier wave receiving channel 4. Associated with the trunk circuit 2 is the alternate frequency oscillation source 5 which serves to supply alternating currents of two frequencies in regular sequence to said trunk circuit for transmission, and the alternate frequency receiving apparatus 6, which receives alternate frequency currents incoming over said trunk circuit and responds thereto to give a ring or other signal indication. rlhe principal elements may now be described in detail.

The alternate frequency source 5 consists of a three-element vacuum tube oscillator 7 having alternating current plate and grid circuits coupled in feed hack relation by a transformer 8'. The frequency of the oscillations produced is determined in well known manner by the tuning of the closed circuit including the primary windng lof the transformer 8 and capacity element 9. An additional condenser 10 is arranged to be connected in parallel with element 9 to change thc tuningr of this circuit and in consequence thereof to change the frequency of the alternating current produced. A. three-element vacuum tube amplifier 11 has its grid filament circuit associated with the secondary winding of the transformer 8 and accordingly serres to amplify the oscillations pro- :licori liv oscillator 7 and to supply the amplified oscillations over a transformer to a circuit 12 adapted to be associated ywith the trunk circuit 2 by means of a relay 13. The plate batterv 14 for the oscillator and amplifier is normally disconnected so that 'hesf devices are inactive. A start relay 15v under control of the operator is provided with tiro lefthand contacts. the front one of which is used to connect up the plate batery and the back one of which closes a circuit from ground through a source 16 of ringing alternating current and the biased polarized relay 17 which controls the tuning of the'/ alternate frequency source;

The alternatefrequency receiving apparatus 6 comprises a three-clement thermionic amplifier 19 connected by a potentiometer 20 to the two series transformers 21 and 22, the primary Winding of each of which is shunted by an antiresonant circuit tuned to the frequency of one of the alternate frequency currents buthaving low impedance relative to its shunted transformer winding for current of the other alternate frequency. rTransformer 21 serves to impress one of the alternate frequency currents on a relay tube 25 which controls the direct current of the upper winding of differentially acting relay 26 and the transformer 22 is in similar @manner related to the lower winding of relay 26. The armature of relay 26 carries a movable contacter engaging at the outer limits of its motion, two stationary contacts 35, through either of which it may complete a circuit from ground through a slow acting relay 36. lf the movable contactor is caused to vibrate at the proper frequency, that is, the frequency of alternation of the two alternate frequency currents, the circuit of relay 36 is in edect maintained open to deenergize the relay 36 and release its armature.

The carrier wave transmitting channel 3 may comprise a three-element amplifier 27 of the vacuum tube type to the output circuit of which is connected a constant current modulating system 28. This modulating system for producing and modulating carrier waves is well known and has been described in the paper by Messrs. Craft and Colpitts entitled Radio Telephony volume 38, page 360, proceedings of the American lnstitute of Electrical Engineers. rThe output circuit of this high frequency n'iodulating system is associated with an antenua for radiating the modulated wave energy to a distant receiving station.

The carrier wave receiving channel 4 comprises a receiving antenna for receiving energy radiated from a distant station, a thermionic detector 29 and a thermionic amplitier 30 connected thereto for transmitting the detected currents to the conductors of trunk 2. rlhe thermionic detecting and amplifying apparatus is of conventional type and needs no further explanation.v The carrier wave transmitting and receiving channels, which are conjugately associated with the trunk circuit 2 through the customary hybrid coil arrangement with the usual net N for maintaining th-e impedance balance, in effect constitute a four-wire circuit connected to the trunk circuit 2. It should be clearly understood that the invention is not limited to radio transmission but that the modulated carrier waves may be guided over a four-wire circuit to the distant station, the four-wire circuit either extending between the local and distant stations or being connected to a two-Wire circuit which does so extend.

ln the case of radio operation, the transmitting and receiving antennae of the local station may be physically widely separated and maybe tuned to operate at widely different carrier frequencies, it being understood that each operates at the same carrier frequency as its cooperating antenna at the distant station.

The circuit of Fig. 3 illustrates a-modified alternate frequency receiving apparatus in which the amplifier 19 and selecting circuits 23 and 24 are replaced by two parallel filters 30 and 31 to each of which an am- `circuit for start relay plifier 32 is connected. Each amplifier 32 has associated in tandem therewith a thermionic relay 33 for controlling the direct curient in the winding of the differentially acting relay 34 which corresponds to 'the relay 26 in Fig. 1.

The relationship of the various parts of the system which have been described and the nature and function of the various other elements may be understood from the following description of the mode of operation of 'the system as a whole.

Assume for example, that a local subscriber desires to communicate with a subscriber associated with a distant exchange, over the carrier transmission channels. When a signal is received over the line circuit of this local subscriber (not shown) the local`opera'tor in responding thereto connects with the subscribers line the cord circuit 1. The operators monitoring apparatus 40 may be connected with the cord circuit 1 by means of the monitoring key' 41. Upon ascertaining that a connection is desired for communication with a subscriber associated/at a distant exchange, the operator inserts the plug 42 of the cord circuit 1 into the jack 43 of trunk circuit 2. This completes a circuit from ground through battery over the sleeve contact of the plug, the sleeve of the jack and relay 44 to ground. Relay 44/energizes and remains energized as long as the plug 42 and jack 43 are connect ed. The left-hand armature of relay 44 is thereby closed on its contact and completes a circuit from ground over the line conductors of a repeating loop of trunk circuit 2, through relay 45 and battery back to ground. Relay 45 energizes and connects up the plate battery 46 of amplifier 27 and the tubes of the constant current modulating system 28, thus rendering each of these tubes active. At the same time, relay 44 pulls up its front right-hand armature contact preparing` a circuit for relay 47. The righthand back armature of relay 44 is also pulled up. The operator thereupon operates a. ringing key 48 to connect a source 49 of alternating ringingl current to trunk circuit 2. This ringing current traverses a bridge path 50 including relay 51 whichTis consequently energized and pulls up both its right-hand and left-hand armatures during the application of the ringing current. The left-hand armature of relay 5l closes a local 15. Relayl 15 in energizing closes its front and back armatures on their respective contacts, the front armature connecting plate battery 14 to the tubes 7 and 11 of the oscillator and amplifierrespectively. The back armature closes a circuit from ground through a 20 cycle alternating current source 16 and the biased polarized relay 17, thus varying the tuning of the oscillator 7 by the introduction of condenser 10 at 20 times per second. The oscillator 7 with the condenser 10 disconnected will produce alternating current of one frequency, for example, 550 cycles and with the condenser 10 connected will produce current of another frequency as, for example, 400 cycles. lt

follows that amplifier 11 will impress upon the circuit l2 a continuous train of oscillations of 400 cyclesfrequency, followed by a train of 550 cycle oscillations and in turn by another train of 400 cycles, these trains occurring in regular sequence at 'the rate of 2() trains of each frequency' per second. Returning to relay 51, the right-hand armature is closed at the same time as its left-hand armature to complete a circuit for rela 13 which disconnects that portion of the trunk circuit 2 adjacent to cord circuit 1 and connects in its stead circuit 12 to apply the trains of alternate frequency currents to trunk circuit 2 for transmission over its outgoing channel. At the same time, relay 13 operates to disconnect the alternate frequency receiving channel 52 to prevent the transmission of a signal back over the calling subsc-ribers line. The alternate frequency currents applied to theY trunk circuit 2 are transmitted overl the hybrid coil through amplifier 27 to the constant current modulating system 28, thereby varying the energy ra- Kdiated from the transmitting antenna in well known manner.

Since the apparatus at the dista-nt exchange may be similar in every respect to that illustrated in Figs. 1 and 2 the course of the modulated signal energy received at the distant station may be considered by noting the operation of the local station apparatus for receiving modulated energy, A modulated wave incident upon the local receiving antenna, causes modulated'currents of corresponding frequency and Wave form to be applied to the thermionic detector 29. These currents are detected, and the detected alternate frequency wave trains are applied by means of amplifier 30 and the hybrid coil connection to the trunk circuit 2. ln considering receiving conditions, it should be noted that the various relays and circuits are all in normal receiving condition as indicated in Fig. 1, the local cord circuit 1 of the receiving operator being disconnected from the trunk circuit 2. The alternate frequency wave trains received over trunk 2 pass to receiving channel and after amplification by amplifier 19 are suppiled to transformers 21 and 22 by the potentiometer connection pedance of the'antiresonant circuit 23 for the wave train of one ofthe two frequencies, substantially all the current of that frequency will be forced to traverse the primary winding of the transformer 21. Since the antiresonantA circuit 24.is of relatively low impedance compared with its shunted 20. As a result of the high imwinding of transformer 22 for currents of the frequency under consideration, the currents which traverse the primary winding of transformer winding 21 will be effectively shunted from transformer'22 by the antiresonant circuit 24. In a similar mannen,

rents and the other relay 25 will similarly respond throughout the duration of the other frequency wave. The two windings of relay 26 which act differentially upon the armature will alternately attract its armature causing its'contactor to vibrate between contacts 35 at a 20 cycle rate, thus maintainino' the circuit of relay 36 effectively open. Ray 36 accordingly deenergizes and releases its armature to complete a circuit for relay 54. 'Relay 54 pulls up its right-hand armature to energize the lamp or other signal 55 and at the same time closes a. locking circuit for itself through its left-hand armature and contact, p

The operator at the receiving exchange noting this signal, inserts the plug 42 of the local cord circuit into the jack 43 of the trunk circuit 2, thereby energizing local cut-off relay 44 to open its back right-hand armature contact and cut off the signal. At the same time, cut-off relay 44 pulls up its right-hand front armature preparing a circuit for relay 47. It further closes its lefthand armature contact to render active the carrier wave transmitting apparatus of.

transmitting channel 3 as described in connection with the operation of the calling station. The operator thereupon connects lier monitoring apparatus 40 to cord circuit 1. When talking currents are impressed upon the cord circuit 1 they are transmitted over trunk circuit 2 and caused to modulate the carrier wave, the energy of which is thereupon transmitted to the distant calling station. The receiving operator having thereby obtained the necessary information completes the desired connection after first calling the desired subscriber in the usual manner and then connecting the local cord circuit 1 to the line of the desired subscriber. The connections between the two subscribers are now completed and communication proceeds in the usual manner.

Should the calling subscriber desire to recall the called subscriber before the connections at the operators stations have been broken, he may communicate the fact to the operator at the calling exchange. The operator applies ringing current from ringing source 49 and the alternate frequency waves received at the called exchange cause, the deenergization of relay 36 whereby the cirravaeav l cuit previously described through relay 47 is completed causing this relay to eneregize and connect ringing source 56 to the cord circuit 1. This ringing current energizes local supervisory relay 57 lto actuate signal 58 in the usual manner and the operator at the called or receiving exchange noting this signal, may thereupon recall the called subscriber. Upon the termination of the conversation as indicated by the lighting of the usual lamps associated lwith the subscribers .line circuits, each operator may disconnect her cord circuit from the subscribers line and from trunk 2 thereby restoring the various circuits to normal condition. n

The operation of the arrangement of Fig. 3 is substantially the same as the operation of receiving apparatus 6 of Fig. 1. Alternate frequency wave trains are received over channelv 52. Filter 30 passes onlyT the wave train of one alternate frequency and filter 31 passes only the wave train of the other alternate frequency. The amplifiers 32 and tliermionic relays 33 operate in` the ordinary manner to actuate relay 34.` The operation of relay 34 will-be understood from the description of the operation of relay 26. An obvious adaptationof this apparatus for code signaling may be made by using the same method to operate the slow release relay at the receiver, the operation of this relay indicating thel desired signal to the operator at the receiving station. It is obvious that this invention may be applied to teledynamic operation generally. A1- though the invention has been described in connection with a specific transmission circuit, it is to be understood that it is not to be limited thereto, but only by the scope of the appended claims.

What is claimed is:

1. A method of carrier wave transmission which comprises modulating a carrier wave by means of a plurality of successively recurring waves of different frequencies to constitute a single signal element.

2. A method of selective transmission which comprises 4transmitting a carrier wave modulated by alternately recurring equal duration trains of two different frequencies to constitute a single signal element.

3. A method of signaling by carrierwaves which comprises modulating a carrier wave by aV plurality of waves of different frequencies successively recurring to constitute a single signal element.

4. A method of signaling by carrier waves which comprises modulating a carrier wave by two waves of different frequencies altervnately repeated to constitute a single signal element.

5. A method of signaling by carrier waves which comprises modulating a carrier wave by a plurality of waves of diiferent frequencies successively recurring, deriving the wave components of different frequencies from the carrier wave and controlling an 1nfg dicator by the joint action -of the derived wave components.

6. A method of signaling by carrier waves which comprises causing a source of current to supply alternately recurring waves of different frequencies, modulating a carrier wave by said alternating recurrent waves,

.deriving the alternately recurring Waves from the carrier wave and controlling an indicator by the joint action of said derived waves.

7. A method which comprises transmitting a carrier wave modulated by successively recurring currents of different frequencies, deriving the currents of different frequencies from the carrier Wave and operating a' controlled device by the cooperative action of the energies of said derived currents.

8. A method which comprises transmitting a carrier wave modulated by successive waves of different frequencies recurring at a definite frequency, deriving the waves of different frequencies from the carrier wave and controlling a device by the derived waves of said frequencies recurring at said denite frequency.

9. A carrier Wave system comprising means to supply a wave train composed of a plurality of waves of different frequencies succeeding each other at a definite rate to constitute a singlesignal element and means for modulating a carrier wave by said train.

10. A carrier wave system comprising a carrier wave channel, means to control a source of energy to supply waves of different frequencies, and means for impressing said waves successively upon said channel at a definite rate to modify a carrier wave several times alternately by said waves to producev a single signal element.

11. A carrier signaling system comprising means for modulating a carrier wave by two'wave trains applied alternately in regular sequence to constitute a single signal element.

12. A carrier wave system comprising means for deriving from an incoming carrier wave non-simultaneous wave trains occurrin in regular sequence and means for contro ling a responsive device by the conjoint action of said derived wave trains.

13. In combination, a modulating element, a source of carrier waves, a source of alternately recurring wave trains of two different frequencies to constitute a single signal element and means for causing said wave trains to operate upon said modulating element to modulate said carrier waves.

14. A signaling system comprising a carrier wave circuit, a low frequency circuit,

said carrier wave'circuit comprising means for detecting carrier waves received thereover to derive alternately recurring Wave trains of different frequencies and means responsive to said alternately occurring detected wave trains to operate a signal associated with said 10W frequency circuit.

15. A carrier wave transmission system comprising a source of carrier waves, a normally inactive source of signaling waves, and a ringing key to simultaneously render said inactive source active and to associate it with said carrier wave source to modulate said carrier waves in accordance with said signaling waves.

16. A receiving circuit, means for impressing thereon currents of two different frequencies, two translating elements adapted to respond to currents of said different frequencies respectively, and means for connecting said elements to said circuit comprising two transformers having their primary windings in series and having each primary winding shunted by a closed loop circuit tuned to the frequency of the current to be transmitted by its shunted winding.

17. A carrier wave system comprising an operators station, a cord circuit thereat, a carrier wave transmission channel having an inactive source of carrier waves, and means responsive to connection of said cord circuit to said transmission 'channel at said operators station to automatically cause said carrier wave source to become active.

18. A radio system comprising a transmitting channel, an oscillator of the electron relay type connected theretoand having its space current source normally disconnected, an operators cord circuit, and means responsive to connection of said cord circuit to said channel to connect said space current source to render said oscillator active.

19. In a signaling system, means for transmitting a carrier wave, means for modulating said Wave at a plurality of frequencies in cyclic order at a definite periodicity of cyclic recurrence in combination with a receiver selectively responsive to the carrier frequency, each of the plurality of frequenciesand the frequency of cyclic recurrence.

20. In a distant control system, mea-ns for` transmitting periodic energy, vmeans for varying said energy at a plurality of different frequencies in cyclic order at a definite periodicity of cyclic recurrence. in combination with a controlled element responsive only when the ener variation is at the definite periodicity o cyclic recurrence.

21. A signal transmission system comprising means for producing and radiating an unmodulated high frequency carrier wave during non-signaling intervals, means for producing a plurality of lower frequency waves, and means for modulatin said high frequency wave in regular per1odic order with said lower frequencyfwaves during signaling' intervals.

22. A signal transmission system comprising means for iroducing a carrier Wave, a ringing key, an means actuated by the actu- Y ation of said key to vary said carrier Wave in cyclic order in accordancewith a plurality of modulating frequencies.

23. n a system for controlling a distant element, means for transmitting carrier Wave energy varied at tvvo frequencies in a1- ternation at a definite rate ofalternation in combination with .selective means whereby the distant element to be controlled is affected in the desiredaiianrger only when the Vcarrier Wave energy, both of the frequencies,

and time rate of alternation y correspond' to certain selective characteristics of said scf lective means.

24. A selective receiver adapted for cori-l trol by energy varied in accordance `with two Wayes of definite frequencies recurring alternately at a definite periodicity comprising means selective to the frequency of the energy, means selective to the frequency of each of the waves, and means selective to the periodicity of alternation.

In Witness whereof, l hereunto subscribe ilngyoname this 24th day of August, A. D.,

PAUL B. MURPiiY. 

